The Gate, a 445,000 square metre complex, is being built in Cairo's Heliopolis district. Eight buildings will intertwine to form the complex. The top floors will be connected by pedestrian bridges, and offer playgrounds and small gardens growing fruit and vegetables. There will also be an infinity swimming pool.

The Gate will include three floors of office space, a three-story shopping mall with four underground levels for parking, and 1,000 'smart' apartments. Each residence will come equipped with motion sensors that adjust temperature and lighting when residents are home.

The interior will feature nine 'mega-trees': cylindrical living walls that will help provide natural ventilation and consume carbon dioxide. The buildings will be partially powered by solar and wind.

Callebaut, a Belgian architect, is known for his greenery-filled structures. He sees The Gate as a small step toward a more sustainable future. 'The main objective behind this project is to raise awareness of green sustainable architecture to fight against global warming to maintain an eco-friendly Earth for our next generation,' Callebaut said.

Callebaut's other projects include a masterplan to revamp an industrial zone in Brussels, Belgium by adding luxury housing, restaurants, shops, office space, and greenhouses. His firm submitted the plan to the local government for review in February.

They're also working on a manta ray-shaped ferry terminal in Seoul, Korea. The designs for that structure, which were unveiled in June, also call for it to be covered in plants.